1. Field of the Invention
The invention relates generally to pulsed radio-frequency transmitting systems and more particularly, to such systems as they apply in the radar arts.
2. Description of the Prior Art
Along with the trend toward higher powered pulsed-radar transmitters, there has also been a need for improved performance of associated MTI (moving target indicator) systems. Among the factors which tend to degrade MTI performance is the transmitter output noise figure. Temporal noise, in particular, is a significant problem in respect MTI performance. This temporal noise manifests itself as variation in the timing of the leading edge ("jitter") of the transmitter RF pulse and to some extent, also the variation of pulsewidth or duration.
The usual radar transmitter includes a pulse modulator of high power capability and an RF generator which operates on a pulsed basis in response thereto. The high-power modulator is supplied from a high-power, rectifier-filter arrangement and sometimes through an electronic regulator circuit. The presence of power supply ripple is a significant cause of the aforementioned temporal noise. Aging of the RF generator itself can introduce temporal noise of a long-term type, however, this has little perceptible effect on MTI performance because it occurs over a relatively long time base, except to the extent that aging may increase sensitivity to power supply ripple. Certain other instabilities in addition to power supply ripple also contribute to the short-term temporal noise which, it is desired, be greatly reduced for the provision of a "stiffer" transmitter RF pulse.
The use of elaborate power supply filtering and regulation is, of course, possible, and does have a beneficial effect, however the adequate filtering and regulation of such a relatively high-powered source is of itself, quite expensive.
The manner in which the combination of the present invention operates to greatly ameliorate the temporal noise problem as aforementioned will be understood as this description proceeds.